This invention relates generally to papermachines used in the making of paper and relates, more particularly, to the means and methods for supporting a web of paper as the web is moved through the papermachine. The invention addressed herein is particularly relevant in the making of tissue paper (i.e. a lightweight paper grade), but can also be used in the making of any grade of paper within a large range of paper grades.
As a web of paper is moved through a papermachine during production of the paper, the web contacts various surfaces of the papermachine components, such as dryer cylinders, transfer rolls and permeable carrier mediums (e.g. fabrics, wires, or felts), which provide support and stability to the moving web. However, there commonly exists open draws between surfaces of adjacent papermachine components through which the web is required to move without contact from any papermachine component. Such an open draw may, for example, be present between the off-running side of a dryer cylinder and a moving carrier medium or an equivalent surface to which the web is transferred from the cylinder or between the off-running end of a moving carrier medium and the surface of a subsequent transfer roll. Consequently, as the web moves through such an open draw, the web is devoid of any external support which would help stabilize the web. It would be desirable to provide an apparatus for use in a region of a papermachine where such an open draw would otherwise be present and which provides support and stability to the web as it moves through the region.
Accordingly, it is an object of the present invention to provide a new and improved means for supporting a web of paper as the web is moved between adjacent components of a papermachine where there would otherwise exist an open draw through which the web is moved and a method of supporting the web as it is moved between the papermachine components and method of supporting the web as it is moved between the papermachine components.
Another object of the present invention to provide a new and improved means for providing support and stability to a web as it moves through a region of a papermachine wherein no external support has heretofore been provided to the moving web as it moves through the region.
Still another object of the present invention is to provide such a means which reduces the likelihood that the web will pull itself apart (due, for example, to the weight and water content of the web) or experience undesirable movements, such as flutter, as the web is transferred between successive components of a papermachine which could result in a web break or adversely affect the quality of the paper being produced.
Yet another object of the present invention is to provide such a means which helps to confine the movement of the web along an intended path of movement thereby reducing the likelihood of a web break as a result of the web moving out of its intended path of movement.
A further object of the present invention is to provide such a means which is particularly well-suited for supporting a web of tissue paper as the web is moved between adjacent components of a tissue machine where there would otherwise exist a open draw.
One more object of the present invention is to provide such a means which is uncomplicated in construction yet effective in operation.
This invention resides in an apparatus and method for supporting a web of paper moving through a transfer region of a papermachine through which region the moving web is transferred from the surface of one component of the papermachine to the surface of a subsequent component of the papermachine.
The apparatus includes an air-permeable sheet supportable in a stationary condition across at least a portion of the papermachine region through which the moving web of paper is transferred from one component of the papermachine to a subsequent component of a papermachine and so that as the web is moved through the papermachine region, the web moves along one side of the air-permeable sheet. Also included within the apparatus are means for creating a zone of sub-atmospheric pressure adjacent the side of the air-permeable sheet opposite the web so that as the web is moved through the papermachine region, the web is biased, by air pressure, into contact with the air-permeable sheet and moves in sliding engagement therealong.
The method of the invention includes the steps of positioning the air-permeable sheet in the stationary condition across at least a portion of the papermachine region and then creating a zone of sub-atmospheric pressure adjacent the side of the air-permeable sheet opposite the web of paper so that as the web is moved through the papermachine region, the web is biased, by air pressure, into contact with the air-permeable sheet and moves in sliding engagement therealong.